The present invention relates to a photographic printing system, and more particularly to a color printing system in which exposure is controlled based on a large area transmittance density of an original film.
In a large scale photographic printing system, a large area transmittance density (LATD) is obtained first by color. Then, based on the LATD, exposure is controlled to provide a desirable print condition. Such an LATD printing system can yield the advantage of providing a print having a favorable density distribution when the print is made from a negative having no difference in density between a principal image, such as a human face, and the whole image of the negative.
Because of variations in negatives provided by customers, it is difficult to make satisfactory density controlled prints from almost all of the customers' negatives with an LATD printing system. As an example, in making a print from a negative including a human figure in a bright background or a human figure in a dark background (a condition generally referred to as having a density failure), or from a negative including an area having a bright color (any one of, or any combination of, red, green, blue, cyan, magenta and yellow) that is too large relative to a principal subject image, such as a human figure (a condition generally referred to as having a color failure), a principal subject image of the negative is exposed too little or to much, or with adverse effect from a color of the major part thereof, resulting in a print having imbalanced color and/or density.
To avoid such an adverse effect caused because of subject failures (density failure and color failure) in the LATD printing system, it has been preferred to inspect negatives prior to making prints from the negatives by the use of the LATD printing system, thereby correcting the exposure for each image frame of an original negative. In recent years, an improved LATD printing system in which exposure is effected with high accuracy has been developed, and has become increasingly popular. The improved LATD printing system measures an original negative to detect densities at a large number of points of the original negative, and classifies the image pattern of the original negative statistically based on the density distribution. The developed LATD printing system effects an exposure obtained from the image pattern, a characteristic value of a specific point or area, and an LATD of the original negative.
However, because conventional LATD printing systems are equipped with no automatic exposure correcting feature for avoiding occurrences of subject failure, it is necessary to provide exposure correcting data by inspecting negatives prior to making prints. Negative inspection is effected by an operator, and exposure correction value data is recorded manually, for example, on a paper tape by means of a so-called notcher-puncher. Such a negative inspection not only requires skill but also is quite inefficient. Accordingly, it is difficult for beginners to effect negative inspection with high accuracy and high efficiency.
It was thought that an automatic exposure correction value determining device for correcting an exposure in accordance with a pattern of image of a negative film should be provided separately from a printer, and attached to a large size of existing printer. In this case, because there is a difference between the processing capability of the printer and the computing ability of such an automatic exposure correction value determining device as being separately provided and in more detail, the speed of computing data for one frame in the automatic exposure correction value determining device is slower than the speed of computing data for one frame in the automatic exposure correction value determining device, which in turn is slower than the speed of printing one frame in the printer. As a result, the adaptation of the automatic exposure correction value determining device lowers the speed of processing of the printer.